(1) Field of the Invention
This invention relates to apparatus for conveying or transporting articles during manufacturing processes, particularly during the manufacture of metal container bodies. More particularly, the invention relates to so-called star wheels that convey such articles in an arcuate path from one point to another.
(2) Description of the Related Art
Star wheels provide one way of conveying articles around an arcuate path and they are used extensively in equipment designed for manufacturing various items, particularly metal container bodies for beverage containers or the like. Star wheels are rotatable wheel-like transporting devices provided with a number of semi-cylindrical pockets around the wheel periphery. Each pocket holds an individual article and conveys it, as the wheel turns, from a feed point where the articles are loaded onto the wheel, to a discharge point where the articles are released.
In order to hold the articles firmly in the pockets during rotation of the wheel to counteract the effects of gravity and centrifugal force, such wheels may be provided with a vacuum system to hold the articles temporarily in place by means of negative air pressure generated between the article and the surrounding surface of the pocket. The vacuum is generally applied as a pocket passes the loading point and released as the pocket passes the discharge point to facilitate removal of the articles from the pockets.
An example of a star wheel of this kind is disclosed in U.S. Pat. No. 5,531,312 which issued to Daniel M. Dickey on Jul. 2, 1996. In this device, vacuum is applied to one or more holes in the peripheral pockets. There is a stationary “valve” connected to a vacuum pump and the “valve” delivers the vacuum to the interior of the wheel. To ensure that there is no loss of vacuum between the valve and the wheel, a spring forces the valve against the wheel. The spring is required to apply a sufficient amount of force so that a reasonably good vacuum seal is provided, but this creates friction and wear and also increases energy costs for operating the apparatus.
Another example of a star wheel of this kind is disclosed in U.S. Pat. No. 7,219,790 which issued to Lino Lanfranchi on May 22, 2007. The device disclosed in this reference is somewhat similar to that of the Dicky patent mentioned above in that a wheel holding the articles rotates adjacent to a stationary plenum to which a vacuum source is connected. Again, friction, wear and high cost of operation are likely to result from this design.
There is therefore a need for a star wheel of this kind that may be operated more efficiently.